Bangbox

Ok, I call this thing simply the bangbox, because that is what it does when activated. Producing loud bangs. It actually is a high energy ignition system. And I think it cannot be built much simpler. This is what it looks like, not yet fit with the large storage capacitor, but only 100nF instead.

This picture shows the bangbox with a micro spark plug as used on small model aircraft IC engines. The plasma extends approx. 3mm from the gap and is really hot.

And this is how it works (click on the schematic for a larger version):
A flyback converter transforms the 12V input to approx. 2-3kV (adjustable, depending on energy storage capacitor capabilities) and charges the capacitor. Through a voltage-doubler circuit another (small) capacitor is charged. This cap is connected to an air spark gap, that connects to the primary of a Tesla transformer. When this gap breaks down, the secondary of the Tesla transformer induces about 15kV, which is superimposed over the voltage of the storage capacitor and causes breakdown of the ignition spark plug. Once ionized, the large current, supplied by the storage cap, flows through the Tesla secondary (resistance well below 0.1 Ohm) to the spark plug. A very similar design is used to ignite xenon short arc lamps or argon ion laser tubes.

These are the two transformers. The left one is the flyback transformer, primary 10 turns of 2 x 0.5mm dia bifilar, secondary 100 turns of 0.3mm dia, 4 layers with layer isolation. The core has an air-gap of 0.5mm. The right one is the Tesla transformer, secondary 20 turns, 2 1/2 layers, primary 4 turns, no core air-gap. The wire is 1mm dia silver plated copper, threaded into a PTFE tubing with 1.1mm inner dia. Both cores were recycled from power transformators, salvaged from blown desktop PC power supplies. They are approx. 40 x 35 x 12mm³ in size and are of N27 material.

You can download the CAD file for this device here.

The circuit has been designed with Target 2001 by Ingenieurbüro Friedrich. They offer a free demo version of this program at their web page http://www.ibfriedrich.com . The demo is only restricted in component count and should be more than sufficient for this circuit. An English language version is also available, as is the documentation.

To be continued as I get hold of a larger capacitor.

09/25/2000

Wow - finally making really big bangs! Last week I obtained a few surplus capacitors for microwave oven - rather cheap. They are rated 1µF at 2100VAC, so they should stand almost 3kV DC. I didn’t want to ruin my small spark plug, so I used two copper wires to form a spark gap. It is about 4mm wide and gets a little bit wider with each bang ;-). It is hard to describe the intensity of the discharges. The repetition rate is about 2Hz, varying slightly. I placed a sheet of paper between the electrodes, just being curious what would happen. The arc rips a hole of about 2mm diameter into the paper, and the flash is still brighter. Next I will try to light a Petromax kerosene lamp with it, because my turbocharger turbine is currently configured to run on propane, but this will be changed one day... So I’ll have to go and get a suitable spark plug capable of a little more power. Taking the above picture was quite difficult because the strong electromagnetic pulse emitted from the bangbox causes my digital camera to trigger itself. After about 30 shots I got the above. But photographing these arcs is somewhat similar to recording the sound of a running turbine - you simply don’t catch the “feeling of it”.

If somebody needs one of these capacitors - I still have some left and will sell them cheap.

Just been experimenting a little bit more with the bangbox: I placed a kleenex, soaked with kerosene, between the electrodes and connected the power. The kerosene lights easily. So I think it should light a turbine combustor as well. Now my ears are ringing - I’ll better put on ear defenders next time.